THERESA May yesterday led a chorus of concerns over allegations that millions of users’ personal information was “harvested” from Facebook and used in US presidential campaigning.

Her office called on the social media giant and Cambridge Analytica – the UK data firm that worked with Donald Trump’s election team – to co-operate fully with an official probe.

A whistleblower claims Cambridge Analytica used personal data about more than 50 million people, taken without authorisation in 2014, to profile individual US voters and target them with political advertisements.

The Prime Minister’s official spokesman said: “It is essential that people can have confidence that their personal data will be protected and used in an appropriate way.”

Britain’s data protection watchdog, Information Commissioner Elizabeth Denham, is investigating some 30 firms’ use of data in political campaigns.

“Canvassing someone’s voting intentions is as old as democracy itself,” he said. “But it is important the public is comfortable with how information is gathered, used and shared in modern political campaigns.”

Legislation now going through Parliament already proposed to give the Information Commissioner new powers, he said.

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Theresa May called on Facebook and Cambridge Analytica to co-operate fully with an official prob

Mr Hancock said it was “outrageous” that Facebook had suspended the social media accounts of whistleblower Christopher Wylie, a former research director at Cambridge Analytica.

He added: “Blocking an account, when we know they don’t act fast enough to block other accounts of obviously outrageous behaviour, shows us that when they need to, they can block things incredibly quickly, and they’re going to have to do a lot more of that.”

Several MPs asked whether the social media strategies may have influenced UK elections or the EU referendum.

Cambridge Analytica allegedly obtained data gathered through an app called thisisyourdigitallife. Hundreds of thousands of users were paid to take a personality test and agreed to academic use of the data.

But the app also allegedly collected their Facebook friends’ data, creating an unprecedented cache of private information.

Facebook last week blocked Cambridge Analytica’s pages on its network while it investigated, but it is accused of not doing enough to warn users and of doing too little to recover and secure their data.

Damian Collins, chair of the Common’s Digital Committee, has said he will call Facebook boss Mark Zuckerberg and Cambridge Analytica head Alexander Nix to give evidence to MPs.

The two companies deny wrongdoing.

Last night Channel 4 News broadcast secretly filmed footage of Cambridge Analytica executives boasting to an undercover reporter that they could entrap politicians with bribes and prostitutes.

The company refuted the allegations. Facebook shares plummeted yesterday in response to the scandal.